Photographic physical developers

ABSTRACT

A NOVEL PHYSICAL DEVELOPER FOR PALLADIUM LATENT IMAGES COMPRISES A REDUCIBLE HEAVY METAL SALT, A COMPLEXING AGENT FOR THE HEAVY METAL IONS, A REDUCING AGENT FOR THE HEAVY METAL IONS AND A CARBOXYLIC ACID COMPLEXING AGENT HAVING A HIGH DEGREE OF SPECIFICITY TOWARDS PALLADIUM IONS.

United States Patent ()1 3,598,587 PHOTOGRAPHIC PHYSICAL DEVELOPERS Joseph S. Yudelson and Barbara F. Dernbach, Rochester,

N.Y., assignors to Eastman Kodak Company, Rochester, N.Y. No Drawing. Filed Apr. 22, 1968, Ser. No. 723,269 Int. Cl. G03c 5/24 U.S. Cl. 96-48 21 Claims ABSTRACT OF THE DISCLOSURE A novel physical developer for palladium latent images comprises a reducible heavy metal salt, a complexing agent for the heavy metal ions, a reducing agent for the heavy metal ions and a carboxylic acid complexing agent having a high degree of specificity towards palladium ions.

This invention relates to novel photographic physical developers. In a particular aspect, it relates to stable physical developers for developing palladium latent images.

Physical development comprises the intensification or development of a latent image by treating the latent image with a developer solution which contains a reducible metal compound and a reducing agent. In physical development, virtually all the metal in the resultant visual image is formed by the selective reduction of metal ions supplied by the reducible metal compound in the developer solution. It is desirable that the physical developer solution be so formulated that it is stable under conditions of storage, but that in the presence of a catalyst, such as the latent image, it decomposes and deposits reduced metal on the catalytic sites. Once a catalytic site is enveloped with metal deposited from the bath, it is essential that the reduced metal be autocatalytic, that is, it too must catalyze the decomposition of the physical developer solution.

Physical development involving silver compounds is well known. However, such processes have not had any substantial commercial application, except in very specialized applications, due to the fact that silver physical developer solutions are extremely unsable. Thus, shortly after a physical developer solution is prepared b mixing silver salts and reducing agents, reduced silver begins to deposit rapidly, so that in a few hours the bath is completely decomposed and is of no practical utility. This type of instability is inherent in silver physical developer solutions since the poor autocatalytic properties of silver metal requires that silver physical developer solutions be formulated so as to be capable of depositing silver very rapidly, if inordinately long development times are to be avoided.

In copending Yudelson et al. application Ser. No. 653,- 025, filed July 13, 1967, there is described a photographic element and process which can be employed with physical developer solutions which are extremely stable under conditions of storage. This system is based on light-sensitive palladium compounds which upon exposure to actinic radiation form catalytic centers or sites for the deposition of metal from these stable physical developer solutions. Unlike silver, the palladium sites formed on exposure catalyze the reduction of metal compounds which have good autocatalytic properties. Therefore, physical developer solutions which are extremely stable under storage conditions can be formulated with such metal compounds and employed in the above-mentioned system, thus avoiding the disadvantages associated with silver physical development. The physical developers which are employed with the palladium photosensitive element of the abovementioned Yudelson et al. application comprise a reducible heavy metal salt, a reducing agent and a complexing or chelating agent which complexes or chelates the 3,598,587 Patented Aug. 10, 1971 reducible heavy metal ions and prevents them from being reduced by the reducing agent in the absence of a catalyst.

While these palladium photosensitive elements and the physical developers which are employed with them provide a physical development system having practical utility, the fact that palladium compound remains in unexposed areas of the element, in many instances prevents all of the advantages of which these systems are capable from being fully realized. Since many of the palladium compounds employed in these photosensitive elements are soluble in the physical developer solution, whereat the palladium ions can be reduced by the reducing agent, the useful life of the physical developer solution is decreased and the possibility of fog formation in non-image areas of the photosensitive element is increased. When palladium compound, present in unexposed areas of the element, is dissolved in the physical developer solution and is there reduced by the reducing agent, the palladium metal thus formed acts as a catalytic center or site for the reduction and deposition of reducible heavy metal ions from the physical developer solution. Since these catalytic centers are present in the physical developer solution itself, the solution can spontaneously decompose once it has been used to develop a palladium photosensitive element. Thus, the stability of these physical developers during and after use is somewhat less than desired. Further, since the palladium compound can be reduced by the reducing agent in the physical developer solution, it is possible for catalytic centers or sites to be formed by such reduction in non-image areas of the element, thus producing background fog.

One method of eliminating these difiiculties is to thoroughly wash the element subsequent to exposure, but prior to development, to remove unexposed palladium compound from the element. However, such washing is undesirable since not only is an additional processing step introduced, but, to be full effective, inordinately long washing times are required.

Therefore, it is an object of this invention to prolong the useful life of physical developer solutions used with palladium photosensitive elements by novel means. I

It is a further object of this invention to prevent the formation of background fog in palladium photosensitive elements by novel means.

It is another object of this invention to provide novel photographic physical developers for the development of palladium latent images in palladium photosensitive elements. I

It is still another object of this invention to provide novel photographic physical developer solutions which do not spontaneously decompose during or after use.

It is yet another object of this invention to provide novel physical developer solutions for palladium photosensitive elements which do not develop background fog in the element.

It is another object of this invention to provide a novel method of developing palladium photosensitive elements Without production of back-ground fog.

The above and other objects of this invention will become apparent to those skilled in the art from the further description of the invention which follows.

In accordance with the present invention, there is incorporated in photographic physical developers for palladium latent image a carboxylic acid complexing or chelating agent having a high degree of specificity towards palladium ions. Thus, the physical developers of our invention comprise a reducible salt of a heavy metal, a complexing or chelating agent for the heavy metal ions derived from the reducible heavy metal salt, a reducing agent for the heavy metal ions, and a carboxylic acid complexing or chelating agent having a high degree of specificity towards palladium ions. By incorporating in the physical developer, in accordance with this invention, the complexing or chelating agent for palladium ions, the palladium ions in unexposed areas of the photosensitive element are strongly complexed or tied up, and are thus protected from reduction by the reducing agent present in the physical developer solution. Thus, reduction of palladium ions in the non-image areas of the element, and the concomitant formation of catalytic centers in these non-image areas, is prevented, thereby eliminating fog formation. Similarly, any palladium ions which may be dissolved into the developer solution from the photosensitive element will be strongly bound by the complexing agent, thus increasing the useful life of the physical developer solution.

The proper selection of a complexing or chelating agent for palladium ions is important if the physical developer is to have the desired properties and characteristics mentioned above. Suitable compleXing or chelating agents should have a high degree of specificity towards palladium ions. In other Words, they should strongly bind palladium ions, thus preventing the reduction of these ions by the reducing agent in the developer solution, yet they should not bind other reducible heavy metal ions present in the developer solution so tightly as to interfere with or retard these other ions from being reduced and deposited on catalytic palladium sites in the photosensitive element. We have found that a group of polyhydrocarboxylic acids have this desired property. The carboxylic acids which have been found useful as complexing or chelating agents for palladium ions in physical developer solution are gluconic acid, saccharic acid and quinic acid. Thus, by employing these complexing or chelating agents in the physical developers of our invention there can be obtained physical developer solutions which not only are stable under conditions of storage, but which remain stable when contaminated with palladium ions, thus prolonging their useful life, and which, additionally, prevent the formation of fog in the non-image areas of the photosensitive elements with which they are used. Other complexing or chelating agents which are known as components in compositions which can be employed as physical developers do not produce the same desirable results when employed in physical developer solutions for palladium photosensitive elements as does this group of carboXylic acid complexing agents. These carboxylic acid complexing agents can be introduced into the physical developer in the form of the acid, or in the form of a water-soluble salt of the acid, e.g., and alkali metal salt of the acid.

In addition to the complexing agent for palladium ions the physical developers of this invention include a reducible salt of a heavy metal, a complexing agent for the heavy metal ions derived from the reducible heavy metal salt, and a reducing agent which, in the presence of palladium catalytic centers, will reduce the heavy metal ions. These components are chosen so that the physical developer solution is stable under ambient conditions, but that in the presence of palladium catalytic sites the heavy metal ions are reduced by the reducing agent.

The heavy metal deposited from the physical developer solution must itself catalyze the further reduction and deposition of heavy metal ions from the solution; in other words, the heavy metal should be autocatalytic. This is necessary in order for a visible image to be developed after the palladium catalytic centers are enveloped by deposited heavy metal. Suitable heavy metals can be selected from Periodic Table Group VIII metals such as nickel, cobalt, and iron, Group VIb metals such as chromium and Group Ib metals such as copper. The reducible heavy metal ions are introduced; into the physical developer as a water-soluble salt. Suitable watersoluble reducible heavy metal salts useful in the physical developers of this invention include heavy metal halides such as cobaltous chloride, cobaltous iodide, ferrous bro mide, ferrous chloride, chromic bromide, chromic chloride, chromic iodide, cupric chloride, etc.; heavy metal sulfates such as nickel sulfate, ferrous sulfate, cobaltous sulfate, chromic sulfate, cupric sulfate, etc.; heavy metal nitrates such as nickel nitrate, ferrous nitrate, cobaltous nitrate, chromic nitrate, cupric nitrate, etc.; heavy metal salts of organic acids such as ferrous acetate, cobaltous acetate, chromic acetate, cupric formate, etc.; and the like. The physical developers of this invention can be based upon a single one of these reducible heavy metal ions, or upon a mixture of more than one of these reducible heavy metal ions.

The complexing agent for the reducible heavy metal ions in the physical developer should tie up the metal ions to such a degree that the ions are not reduced spontaneously in the presence of the reducing agent. However, the complexing agent should not bind the metal ions so tightly that they will be unable to be reduced by the reducing agent in the presence of palladium catalytic sites. Any complexing agent which satisfies these criteria is useful in the practice of the present invention. A preferred group of complexing agents are the organic carboxylic acids, such as maleic acid, lactic acid, succinic acid, citric acid, aspartic acid, glycolic acid, and the like. In some instances, the car-boxylic acid complexing agent for palladium ions will also be a suitable complexing agent for the reducible heavy metal ions, thus eliminating the need for two separate complexing agents. However, it is preferred that separate complexing agents be employed because the complexing agents for palladium ions are of relatively low solubility. This limits the concentration obtainable in developer solutions in which these carboxylic acids are employed as the sole complexing agent. If a separate complexing agent for the reducible heavy metal ions is employed, heaving a lower molecular weight and a greater solubility than the complexing agent for palladium ions, then physical developer solutions can be formulated having greater concentration, and hence, longer useful life. The carboxylic acid complexing agent for the reducible heavy metal ions can be introduced into the physical developer as the acid itself or as a watersoluble salt of the acid, e.g., an alkali metal salt of the acid.

The reducing agent can be any compound which pro vides a ready source of electrons for the reduction of the heavy metal ions in the physical developer and which does not otherwise interfere with the development of the palladium latent image. Suitable reducing agents include formaldehyde, hypophosphites such as sodium hypophosphite, hydrosulfites such as sodium hydrosulfite, borohydrides such as potassium borohydride, borane amines such as dimethylborane amine, and the like water-soluble reducing agents for heavy metal ions.

Physical developers and physical developer solutions of this invention can be prepared merely by mixing the various components. The components can be mixed in the dry state, and then water can be added when the developer solution is desired for use. Alternatively, because of the stability of these developer solutions, the various components can be added to water prior to the time the developer solution is to be used. Although the order in which the components are added is not critical, it is preferred that the reducible heavy metal salt and the complexing agent therefor be present in solution before the reducing agent is added.

In addition there can be added to the physical developer solutions, in accordance with usual practices, a variety of other materials to facilitate maintenance and operation of the developer and to improve the quality of the developed image, such as buffers, preservatives, thickening agents, brightening agents, and the like.

It has been found that when a minor amount of stannous ions are added to the developer solution in the presence of palladium ions an improvement in image tone and an increase in speed is obtained over developer solutions which do not contain stannous ions. The stannous ions can be introduced into the physical developer as a Water-soluble salt, e.g., stannous chloride, stannous sulfate, etc. The necessary palladium ions can be derived from the palladium ions can be added independently to the developer solution in the form of a soluble salt or complex.

The proportions in which these various components of the physical developer are present in the developer solution can vary over a wide range. Typically, the complexing agent for palladium ions can be present in amounts of from about 0.3 mole to about moles per liter of solution. Concentrations of from about 1 mole to about 5 moles per liter are preferred. Suitable concentrations of reducible heavy metal salt can range from about 0.01 mole to about 1.0 mole of metal salt per liter of solution. The upper limit of concentration is controlled by the solubility of the particular metal salt employer. Preferably, the solution is about 0.1 molar to about 0.3 molar with respect to the heavy metal salt. The relative proportions of metal salt and complexing agent are dependent upon the particular heavy metal salt or salts and the particular complexing agent or agents which are employer. As a general rule, sufiicient complexing agent should be incorporated to tie up the reducible heavy metal ions which are in solution and to lessen the tendency of these metal ions to be reduced prior to use of the developer solution. Depending upon the particular heavy metal salt and the particular complexing agent which is employed, the amount of complexing agent present typically can vary from about 0.2 mole to about 10 moles of complexing agent per mole of metal salt present. Typically, the reducing agent can be present in amounts from about 0.1 mole to about 5 moles of reducing agent per mole of metal salt present in the solution. In order to permit the developer solution to be utilized for its maximum life, at least one equivalent of reducing agent should be present in the solution for each equivalent of reducible heavy metal salt.

It has been found that the pH at which the physical developer solution is maintained affects both the stability of the solution itself and the quality of the image which is obtained from the physical developer solution. Thus, if the solution is moderately alkaline, i.e., if it has a pH of about 8 to about 11, the solution is more stable and image quality is improved. It is preferred to operate the developer solution at a pH of between about 8.5 and 9.5. The solution can be brought to a pH within the desired range by addition of appropriate amounts of a suitable basic material; for example, ammonium hydroxide and/or sodium hydroxide. Other bases, known to those skilled in the art, can be substituted for these compounds. The solution can be maintained at the desired pH by incorporation therein of a suitable buffering system. A mixture of sodium carbonate and sodium bicarbonate is an example of a suitable buffering system. Other suitable buffers will be readily apparent to those skilled in the art.

The light-sensitive elements with which the physical developers of the present invention are used comprise a light-sensitive palladium compound carried on or imbided in a support. Typical of such light-sensitive palladium compounds are those having the general formula where L is a ligand, e.g., a halogen ligand such as bromine, chlorine, or iodine, a carboxylic acid ligand such as a malonate group, an oxalate group, etc., an aromatic ligand such as phenol, styrene, naphthol, etc., a nitrogen ligand such as ammonia, an amine such as methyl amine, ethyl amine, benzyl amine, propane diamine, tetraethylene pentamine, aminoethanol, methylaminoethanol, aminonaphthol, bipyridine, phenanthroline, ethylene diaminetetraacetic acid, etc., a nitrile such as nitrilotriethanol, benzonitrile, etc., an imine such as iminodiethanol, an oxime such as salicylaldoxime or hydrazide such as benzhydrazide, a phosphorous ligand such as triarylphosphine, trialkylphosphine, etc., an arsenic ligand such as triarylarsine, trialkylarsine, etc., an antimony ligand such as triarylantimony, trialkylantimony, etc., and the like; M is an ion such as a hydrogen ion, an inorganic acid ion such as a chloride ion, a bromide ion, an iodide ion, a sulfate ion, a nitrate ion, a phosphate ion, etc., an organic acid ion such as an acetate ion, an acrylate ion, an oxalate ion, a malonate ion, etc., a metal ion such as a sodium ion, a potassium ion, a calcium ion, a strontium ion, an aluminum ion, etc., an onium ion containing such atoms as nitrogen, phosphorous or sulfur such as a quaternary ammonium ion, an quaternary phosphonium ion, a tertiary sulfonium ion, etc., and the like, or M can be a [Pd(L) group; x is an integer of from 0 through 4; y is an integer of from 1 through 4; z is an integer from 0 through 2, and x and z are not 0 at the same time.

Typical of light-sensitive palladium compounds having the above general formula are: potassium palladous chloride, palladium ethylenediamine dichloride, palladium di(triphenylphosphine)dichloride, palladium tetrammine dichloride, palladium diammine oxalate, palladium oxalate, potassium palladium oxalate, and the like.

Reference is made to Yudelson et al. copending application Ser. No. 653,025, filed July 13, 1967, for a detailed description of suitable light-sensitive palladium compounds and elements incorporating them, and for the manner in which such elements are prepared and used. In the practice of this invention, an exposed palladium photosensitive element containing a palladium latent image in the form of palladium catalytic centers or sites, is contacted with a bath of a physical developer solution of our invention, for example, by immersion therein, for a period of time sufficient to produce an image of desired density. The time required to deposit a satisfactory heavy metal image on the element can vary from several seconds to several hours, depending upon such factors as the composition of the particular developer solution being employed, the density of heavy metal image desired, the temperature of the bath, etc. Satisfactory images can be produced from developer baths at room temperature (20 C.) or at elevated temperatures up to C. Increasing the bath temperature increases the rate of development, but decreases the useful life of the bath since at higher temperatures the developer solution decomposes more rapidly. Bath temperatures of from about 30 C. to about 60 C. have been found particularly useful.

The following examples are included for a further understanding of the invention.

EXAMPLE 1 A physical developer solution is prepared having the following composition:

Sodium hypophosphite-H O (42.8 g.) 0.4 Gluconic acid (50.0 g.) 0.25

The nickel chloride, malic acid, and gluconic acid are added to 500 ml. of water and then one mole of sodium hydroxide, in solution, is added to neutralize the acids and bring the pH to approximately 5. Concentrated ammonium hydroxide is then added to raise the pH of the solution to 9.0. Next the sodium hypophosphite is dissolved in 200 ml. of water and added to the above solu tion. The volume of the solution is adjusted to one liter by addition of water. A strip of gelatin coated poly(ethylene terephthalate) support (350 ml. of gelatin/ft?) containing approximately 30 mg. of potassium palladium oxalate per ft. is exposed through a line copy negative to a strong tungsten source for 30 seconds and then is immersed in this physical developer solution at room temperature for approximately one minute. A high quality black image appears in the exposed areas of the EXAMPLE 3 A physical developer solution is prepared having the following composition:

Mol/l. Nickel chloride-6H O (46.0 g.) 0.2 Malic acid (53.6 g.) 0.4 Sodium hypophosphite-H O (31.0 g.) 0.3

Gluconic acid (50.0 g.) 0.25 Ammonium chloride (20.0 g.) 0.4

The solution is adjusted to a pH of 9.0 with sodium hydroxide. A strip of the film described in Example 1 is exposed through a line copy negative to a black light source (eight 8-watt BL tubes, 2 /2 inches from the print) and is developed by immersion in this physical developer solution for approximately one minute. A high quality black image appears in the exposed areas of the film while the unexposed areas remain clear.

EXAMPLE 4 Following the procedure of Example 1, a physical developer solution is prepared having the following composition:

Mol./l. Nickel chloride-6H O (23.0 g.) 0.1 Lactic acid (36.0 g.) 0.4 Sodium hypOphosphite-H O (20.2 g.) 0.2

Gluconic acid (50.0 g.) 0.25 Ammonium hydroxide (conc.) (35.0 ml.) 0.5

A physical developer solution is prepared as described in Example 4, except that the gluconic acid is omitted.

Shortly after it has been used to develop a strip of film in the manner described in Example 4, it begins to spontaneously decompose at room temperature.

EXAMPLE 6 Following the procedure of Example 1, a physical developer solution is prepared having the following composition:

Mol/l. Nickel chloride-6H O (23.0 g.) 0.1 Sodium succinate (108.0 g.) 0.4 Sodium hypophosphite-H O (20.2 g.) 0.2

Gluconic acid (50.0 g.) 0.25 Ammonium hydroxide (conc.) (35.0 ml.) 0.5

The final pH of the solution is 9.0. Results similar to those described in Examples 1, 2 and 4 are obtained when this developer solution is used to process a strip of waterleaf stock paper impregnated with potassium palladous chloride which has been exposed to a 350 watt mercury are for one minute at a distance of 14 inches. Omitting the gluconic acid causes the developer to become un- 8 stable and begin to decompose shortly after it has been used one time. Omitting the ammonium hydroxide (but retaining the gluconic acid) gives images of very low density.

EXAMPLE 7 Following the procedure of Example 1, a physical developer solution is prepared having the following composition:

Mol/l. Ferrous chloride-4H O (20.2 g.) 0.1 Citric acid (monohydrate) (84.0 g.) 0.4 Sodium hypophosphite-H O (20.2 g.) 0.2 Gluconic acid (50.0 g.) 0.25 Ammonium hydroxide (25.0 ml.) 0.25

The final pH of the solution is 9.0. Results similar to those described in Examples 1, 3 and 4 are obtained when this developer is used to process a strip of the exposed film material described in Example 6.

EXAMPLE 8 Following the procedure of Example 1, a physical developer solution is prepared having the following composition:

Mol/l. Nickel chloride-6H O (23.0 g.) 0.1 Malic acid (53.6 g.) 0.4 Sodium hypophosphite-H O (20.2 g.) 0.2

Saccharic acid (50.0 g.) 0.25 Ammonium hydroxide (conc.) (35.0 ml.) 0.5

The final pH of the solution is 9.0. A strip of gelatin coated poly(ethylene terephthalate) support containing approximately 15 mg. of potassium palladium oxalate per ft. is exposed through a line copy negative to a fluorescent light source as described in Example 3 and is then immersed in this solution for one minute at room temperature. A high quality black image appears in the exposed areas of the film, whereas the unexposed areas remain clear. After use, the developer solution is heated at C. It begins to show signs of spontaneous decomposition only after being maintained at this temperature for 48 hours. A gluconic acid type bath which has been used and incubated under the same conditions begins to decompose after 24 hours.

EXAMPLE 9 A series of physical developer solutions at pH 9.0 are prepared in which the following components were kept at the levels indicated:

Mol/l.

Nickel chloride 0.1 Sodium hypophosphite 0.2 Ammonium hydroxide 0.5

TABLE I Gluconic Malic acid acid Time (molar) (molar) (minutes) 9 EXAMPLE 10 Following the procedure of Example 1, a physical developer solution is prepared having the following composition:

Mol/l. Cobalt chloride 0.1 Nickel chloride 0.1 Malic acid 0.4 Sodium hypophosphite 0.2 Gluconic acid 0.25 Ammonium hydroxide 0.5

The final pH of the solution is 9.0. A strip of gelatin subbed poly(ethylene terephthalate) support is coated with poly (vinyl alcohol-co-vinyl anthranilate-co-vinyl succinate) in which the anthranilate and succinate group are each present to the extent of approximately 10 mole percent. (This polymeric binder was prepared by the procedure described in Example 2 of Smith and Copenhagen US. patent application No. 723,279 entitled Photo graphic Elements Containing Synthetic Polymeric Vehicles filed Apr. 22, 1968). The dry coverage of the coating is 200 mg./ft. The coating is imbibed for 10 minutes with a 0.5 percent solution of potassium palladium oxalate, the pH of which has been lowered to 2.8 with oxalic acid. After drying, the film contains 53 mg./ft. of potassium palladium oxalate. This film is exposed through a line copy negative to a strong tungsten source for sec onds and is then developed by immersion for minutes at 50 C. in this solution. A metallic deposit forms in the exposed areas of the film. Analysis of the deposit shows that the nickel to cobalt ratio in the coating is virtually identical with the proportions of these ions in the developer solution.

A similar procedure is performed with a physical developer solution having the following composition:

Mol/l. Cobalt chloride 0.2 Nickel chloride 0.1 Malic acid 0.4 Sodium hypophosphite 0.2 Gluconic acid 0.25 Ammonium hydroxide 0.5

The final pH is 9.0. Analysis of the resulting metal deposit on the film shows that the ratio of nickel to cobalt in the coating is almost identical with the proportions of their ionic concentrations in the developer solution. Both developer solutions are completely stable after use at room temperature.

EXAMPLE 1 1 Following the procedure of Example 1, a physical developer solution is prepared having the following composition:

Mol/l. Ferrous chloride 0.1 Nickel chloride 0.1 Malic acid 0.4 Sodium hypophosphite 0.2 Gluconic acid 0.25 Ammonium hydroxide 0.5

EXAMPLE 12 This example illustrates a developer composition which allows for very rapid processing of exposed potassium palladium oxalate film. A physical developer solution is prepared having the following composition:

Mol/l. Nickel chloride 0.4 Gluconic acid 1.75 Sodium hypophosphite 0.4

Sodium hydroxide is added to raise the pH of the solution to 5, and then ammonium hydroxide is added to raise the pH to 9.0. This required approximately 50 ml. of concentrated ammonium hydroxide solution. To this solution is added a sodium alginate thickening agent (Kelgin MV, Kelco Co.) so that the developer composition contains approximately 10 percent of the thickener by weight. A strip of gelatin-subbed poly(ethylene terephthalate) support coated with poly(vinyl alcohol-co-vinyl anthranilateco-vinyl succinate), having the composition described in Example 10, is imbibed with potassium palladium oxalate, dried, and exposed through a test strip negative to the fluorescent light source of Example 3. It is then immersed in the developer composition described above for five seconds, and is then placed between two infrared lamps (GB 250 watt) for five seconds. There is developed on the film strip 8 to 9 steps (0.15 Log E). There is no fog in the unexposed areas of the film strip and the developer solution is completely stable after use.

EXAMPLE 13 This example illustrates a physical developer which is very active at moderate temperatures (50 C.). It is useful in preparing mirror-like images which contain large coverages of nickel, i.e., 500 mg./ft. or more. A physical developer solution is prepared having the following composition:

Mol/l. Nickel chloride 0.1 Gluconioacid 0.65 Sodium hypophosphite 0.1

Sodium hydroxide is added to raise the pH to 3.0, after which approximately ml. of concentrated ammonium hydroxide is added to raise the pH to approximately 9. At this point the following buffer system is added:

'Mol/l. Sodium carbonate 0.1 Sodium bicarbonate 0.1

This buffer system maintains the pH at 9.2. If it were not present, the pH of the bath would drop rapidly with use, causing a lowering of the activity of the bath. A strip of gelatin-subbed poly(ethylene terephthalate) support coated with poly (vinyl alcohol-co-vinyl anthranilateco-vinyl succinate), having the composition described in Example 10, is imbibed with potassium palladium oxalate, dried, and exposed through a test strip negative to the fluorescent light source of Example 3. The exposed strip is then immersed in this developer solution for 5 minutes, washed and dried. There is no fog and the image areas are coated with a heavy mirror-like layer of nickel.

EXAMPLE 14 Following the procedure of Example 1, a physical developer solution is prepared having the following composition:

Mol/l. Nickel chloride 0.1 Malic acid 0.4 Quinic acid 0.25 Sodium hypophosphite 0.2

EXAMPLE 15 A physical developer solution is prepared having the following composition:

Mol/l. Nickel chloride 0.1 Malic acid 0.4 Gluconic acid 0.25 Sodium hypophosphite 0.2

Stannous chloride 0.022

The pH of the solution is adjusted to 9.0 by addition of sodium hydroxide and then ammonium hydroxide. Palladium ion is then added to portions of this solution in the form of either potassium palladium oxalate, palladium oxalate, or palladium chloride in amounts ranging from 15 mg. to 1.5 g./l. After this addition, the solutions are set aside and aged at room temperature for 7 days. Strips of gelatin-subbed poly(ethylene terephthalate) support coated with poly(vinyl alcohol-co-vinyl anthranilate-co-vinyl succinate) are imbibed with potassium palladium oxalate, dried and exposed through a test strip negative to the fluorescent light source of Example 3 for 30 seconds. They are then immersed in the aged developer solutions described above for 3 minutes, washed and dried. The exposed strips all show an increase in speed of approximately four steps (0.15 Log E) as compared with the results obtained in a developer which does not contain the stannous chloride and the palladium ion.

The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

What is claimed is:

1. A photographic physical developer for palladium latent images comprising a water-soluble salt of a reducible heavy metal, a complexing agent for heavy metal ions derived from the reducible heavy metal salt, a reducing agent for heavy metal ions and a carboxylic acid complexing agent for palladium ions selected from the group consisting of gluconic acid, saccharic acid, and quinic acid.

2. A physical developer as defined in claim 1 wherein the reducible heavy metal salt is a salt of a metal selected from the group consisting of nickel, cobalt, iron, copper and chromium.

3. A physical developer as defined in claim 1 wherein the reducible heavy metal salt is a nickel salt.

4. A physical developer for palladium latent images comprising a water-soluble nickel salt, malic acid, a hypophosphite and gluconic acid.

5. A photographic physical developer solution for palladium latent images comprising an aqueous solution of a water-soluble salt of a reducible heavy metal, a complexing agent for heavy metal ions derived from the reducible heavy metal salt, a reducing agent for heavy metal ions and a carboxylic acid complexing agent for palladium ions selected from the group consisting of gluconic acid, saccharic acid, and quinic acid.

6. A physical developer solution as defined in claim 5 wherein the reducible heavy metal salt is a salt of a metal selected from the group consisting of nickel, cobalt, iron, copper and chromium.

7. A physical developer solution as defined in claim 6 wherein the solution additionally comprises a water-soluble stannous salt.

8. A physical developer solution as defined in claim 6 wherein the solution is at a pH of between about 8 and about 11.

9. A physical developer solution as defined in claim 6 wherein the solution is at a pH of between about 8.5 and about 9.5.

10. A physical developer solution as defined in claim 8 wherein the reducible heavy metal salt is a nickel salt.

11. A physical developer solution as defined in claim 8 wherein the reducible heavy metal salt is a mixture of salts of nickel and cobalt.

12. A physical developer solution as defined in claim 8 wherein the reducible heavy metal salt is a mixture of salts of nickel and iron.

13. A physical developer solution as defined in claim 10 wherein the complexing agent for palladium ions is gluconic acid.

14. A physical developer solution as defined in claim 10 wherein the complexing agent for palladium ions is saccharic acid.

15. A physical developer solution as defined in claim 10 wherein the complexing agent for palladium ions is quinic acid.

16. A physical developer solution for palladium latent images comprising an aqueous solution, at a pH of between about 8.5 and about 9.5, of a water-soluble nickel salt, malic acid, and hypophosphite, and gluconic acid.

17. A method for physically developing palladium latent images which comprises contacting a photosensitive element containing a palladium latent image with a photographic physical developer solution comprising an aqueous solution of a water-soluble salt of a reducible heavy metal, a complexing agent for heavy metal ions derived from the reducible heavy metal salt, a reducing agent for heavy metal ions and a carboxylic acid complexing agent for palladium ions selected from the group consisting of gluconic acid, saccharic acid, and quinic acid.

18. A method as defined in claim 17 wherein the reducible heavy metal salt is a salt of a metal selected from the group consisting of nickel, cobalt, iron, copper and chromium.

19. A method as defined in claim 18 wherein the physical developer solution is at a pH of between about 8 and about 11.

20. A method as defined in claim 19 wherein the physical developer solution is at a temperature of between about 30 C. and about 60 C.

21. A method for physically developing palladium latent images which comprises contacting a photosensitive element containing a palladium latent image with a physical developer solution comprising an aqueous solution, at a pH of between about 8.5 and 9.5, of a water-soluble nickel salt, malic acid, a hypophosphite and gluconic acid.

References Cited FOREIGN PATENTS 745,572 11/1966 Canada 96-48PD OTHER REFERENCES Chemistry of the Metal Chelate Compound, Martell & Calvin, Prentice-Hall, p. 296, 1956.

NORMAN G. TORCHIN, Primary Examiner I. L. GOODROW, Assistant Examiner 

